Rivers bully bugs, pushing them to and fro, but the invasive hemlock woolly adelgid is exacting revenge.

After an adelgid outbreak decimated eastern hemlock trees along a headwater stream in North Carolina, researchers expected river surges. Eastern hemlock trees live along riverbeds, sopping up water from the soil year-round, so fewer hemlocks should mean more water seeping into streams.

Instead, the watershed shrank, with its annual flow dropping by 8 percent in less than decade, scientist report June 7 in Ecohydrology. The team expects the decline to continue as rhododendrons and other replacement vegetation that sap more water from the ground than hemlocks take over the vacant land.